The development of deep, rectangular jig pans for the recovery of gold, or other heavy values, from wet alluvial sands has been hampered in the past by the tendency of hard cake, loaded with gold particles, to form on the bottom and on the four walls of the pan by the compaction and dewatering of the suspended solids of the slurry.
Now I have found that the formation of this obdurate hard cake is avoided and the recovery of gold values is significantly improved by a combination of:
1. a rectangular pressurized water manifold spaced slightly above the plane of the pan bottom and provided with at least one row of jet orifices directed at the bottom;
2. four steeply sloped walls at a dihedral angle of about 65.degree. with the plane of the open top of the pan;
3. a V-bottom with its valley aligned parallel to the direction of flow of the slurry;
4. a broad skimmer blade on the spillway gate, oriented coplanar with the surface of the slurry and directed backwardly against the flow; and
5. a connecting rod in the drive train which is resiliently biased, in thrust and in pull directions, by adjustable spring means.
The reciprocating motion is purely linear, horizontal and perpendicularly transverse to the direction of flow of the aqueous/slurry of gold-bearing sand or gravel through the pan. Simultaneously, the finest gold particles, 300M and 400M, which are normally lost in the tailings, are recovered from 12M sands in high yields of 96% and 93%, respectively, without resort to amalgamation.
The closest prior art device known to me is U.S. Pat. No. 171,747 issued on Jan. 4, 1876 to J. M. Thompson, which teaches a deep, rectangular pan which, in plan view, is more elongated than my pan. The Thompson pan is vertically supported on 4 wobble pins allowing the pan freedom to reciprocate in any combination of simultaneous transverse and longitudinal motions. The effective length of the wobble pins is equal to the radius of curvature of the surface of a sphere on which is scribed the locus of the track of any given point of the moving pan. Hence the motion of the Thompson device conforms to tracings on a spherical surface, not on a plane surface, hence it is not linear motion, although Thompson states in his patent that it is linear. The longitudinal motion backward is slow; forward it is fast, each fast stroke terminating in a percussive stop as the pan strikes a rigid, stationary buttress. The percussive jolts progressively advance the load of sand or gravel forwardly in the pan. Thompson states that his device processes the gravel or sand either dry or in aqueous suspension, however, there is no teaching of the addition of the water, no water manifold, no skimmer blade on the spillway gate, no transverse linear motion. All other rectangular pans of the prior art of which I am aware and cite herein are shallow pans or riffle tables.
U.S. Pat. No. 452,676 issued to F. Manuel, et al, on May 19, 1891, teaches an enclosed deep pan, a circular cone, with its axis of rotation laid horizontal, for the concentration of an aqueous slurry. The ore slurry is fed overhead at the large diameter end of the pan. The slurry of tailings is withdrawn through a sluice gate in the small diameter end wall. The bottom of the conical pan is provided with a longitudinally oriented semicircular cylindrical trough with a screw conveyor fitted therein to move the concentrated values backwardly toward a sluice gate in the large diameter end wall, that is, counter-current to the direction of flow of the slurry. The motion of the pan is a combination of: 1--reciprocal axial rotation of the cone, 2--reciprocal cantilevered rocking of the cone, end for end, above a fulcrum provided near its large diameter end wall, and 3--vertical percussive jolts. Water is introduced in the slurry feed and also through a horizontal pipe manifold coaxial with the conical pan and positioned above the level of the surface of the slurry. The orifices in the pipe manifold are directed radially from the pipe in all directions along its length. As compared with the disclosure of the present invention: the pan is not rectangular; the manifold is not rectangular and it is not spaced slightly above the bottom of the pan with jet orifices directed downwardly at the bottom; no skimmer blade is provided in the spillway sluice gate; the reciprocating motion is not linear.
U.S. Pat. No. 1,421,264 issued to R. Le Roy on June 27, 1922. As in the preceding patent to Manuel, et al, this patent teaches a deep pan, conical in shape, with its axis of rotation laid horizontal. In this case, the upper portion of the cone is omitted and is left open. The pan reciprocates in an axial rotational rocking motion of the cone. The ore slurry is fed at the small diameter end of the pan and the tailings slurry overflows over spillway gates on both sides at the large diameter end of the pan. The values concentrate is withdrawn through a valve near the bottom of the large diameter end wall. Special ram means is provided in this valve to break up the compacted cake that forms in this valve and for some distance inside the pan. Secondary pressurized water is introduced coaxially of the conical pan through a horizontal pipe manifold positioned beneath the surface of the slurry. As in the preceding patent the orifices in the pipe manifold are directed radially from the pipe in all directions. As compared with the disclosure of the present invention: the pan is not rectangular; the manifold is not rectangular and is not spaced slightly above the pan bottom with jet orifices directed downwardly at the bottom; no skimmer blade is provided in the spillway gates; the reciprocating motion is not linear.
The advantage of the deep jig pan over the shallow riffle board is its high feed rate capacity and its ability to handle aggregate of wide range of particle size. This eliminates the need for pre-screening the ore for separation into fractions of smaller range of particle size, each of which size requires a different set of panning conditions usually carried out on separate riffle boards.
Prior art patents relating to shallow pans and riffle boards are much more numerous than the deep pan patents described above. With shallow pans and riffle tables the water is introduced via an overhead outlet to the ore feed as is taught in:
______________________________________ U.S. Pat. No. Issue date Inventor(s) ______________________________________ 433,983 Aug. 12, 1890 D. P. Hatch, et al 479,744 July 26, 1892 W. M. Jewell 604,061 May 17, 1898 W. E. Mendenhall 2,077,476 Apr. 30, 1937 H. E. T. Haultain 4,150,749 Apr. 24, 1979 H. W. Stevens 4,319,985 Mar. 16, 1982 W. M. Hibbard ______________________________________
Of these patents, pure linear motion is taught only in Mendenhall and in Stevens. Pendulum arc transverse motion is taught in Hatch, et al, in Jewel, and, in the case of Haultain, the pendulum arc in both transverse and longitudinal combined motions, with a forwardly-directed jolt in addition. Thus, the Haultain movement is traced on the concave interior of a spherical surface as compared with the exterior convex surface of the sphere ascribed above to the Thompson patent. In the case of Hibbard the riffle board is motionless.
In the Mendenhall patent the tray carriage reciprocates linearly on stationary rollers. In the Stevens patent a Wilfley table (see Elements of Chemical Engineering by Walter L. Badger and Warren L. McCabe, second edition, (1936) McGraw-Hill Book Co. Inc., New York, pp. 585-6) is used which carries parallel cleats terminating along a diagonal line of the table. The table is tilted so that the slurry flows from the high corner to the low corner in the direction of the diagonal line. The linear motion of reciprocation is parallel to the direction of the riffles, hence the motion is not horizontal and also it is oblique to the direction of slurry flow, not perpendicularly transverse. The table reciprocates on linear ball bearing races which are inclined from horizontal.
The 3 deep pan patents previously discussed herein provide some insight into the hard cake problem. In Thompson, for example, no hard caking is mentioned and no means is provided specifically to avoid it. Thus it may be presumed that no caking was encountered, perhaps: (a) because the device was tested only with dry sand and not with the aqueous slurry, or (b) because the longitudinal percussive jolts were adequate to keep the pan scrubbed clean.
The other two deep pan patents relate to cone-shaped pans wherein means is specifically provided to withdraw compactly caked values concentrate from the bottom of the pan. In the Manuel patent such means consists of a longitudinal trough in the bottom of the pan with a screw conveyor fitted therein to move the concentrated values counter-current to the flow of the main body of slurry. In this case the percussive jolts are downthrusts, with largest amplitude at the large diameter end of the pan. The jolts augment the force of gravity and hence the compacting power of the weight of the overburden, more so at the large diameter end than elsewhere. This aggravates the caking problem the most, precisely at the location of the values drain opening.
In the Le Roy patent the main body of slurry and the concentrated values move concurrently toward the large diameter end of the pan. There a special drain valve for the concentrated values is provided with a coaxial ram rod which extends through the valve for some distance into the body of the pan in order to break up the cake and keep the valve passageway clear. Furthermore, the drain opening is shielded from obstruction by a length of pipe extending from the opening into the body of the pan. The free end of this pipe is cut at an acute angle and is oriented with its longest length at the zenith of the opening. This provides a canopy shielding the sediment below it from compaction by the weight of the overburden.
Thus, in the prior art there is no combination of these five essential elements of this disclosure: (1) a deep rectangular pan with 4 steep walls sloped at a dihedral angle of about 65.degree., (2) a V-bottom in the pan with the valley aligned parallel to the flow of the slurry, (3) pure linear horizontal transverse reciprocation, (4) a spillway gate with a broad skimmer blade thereon directed backwardly against the flow of the tailings slurry and coplanar with the surface thereof, and (5) a resiliently biased connecting rod in the drive train in which the compression of the spring is adjustable for fine tuning to the load versus the reciprocation frequency combination.
It is an object of the invention to increase the ore handling capacity of the jig pan concentrator.
It is another object of the invention to improve the efficiency of the jig pan concentrator in the recovery of gold from 12M sand.
It is still another object of the invention to overcome the caking problem of the linearly reciprocating rectangular jig pan concentrator.
It is still another object of the invention to provide a fine tuning adjustment in the spring biasing of the drive train to compensate for the cycle phase retardation caused by the viscous drag and slushing of the slurry in the pan and thereby to reduce the high stress loads occurring during the stroke reversals, when acceleration and deceleration is at its maximum.
These objects are successfully accomplished in the herein disclosed device.